As shown in FIG. 1, a prior art amorphous silicon solar cell is illustrated generally as 8 and comprises a transparent insulating substrate 1, a transparent electrically conductive layer 2 and a semiconductor photoelectric conversion laminate 6 composed of a p-type amorphous silicon layer 3, an i-type amorphous silicon layer 4, an n-type amorphous silicon layer 5, and an aluminum electrode 7 acting as the back contact. This configuration is practically used as a photoelectric conversion device capable of being produced at a relatively low cost. Such an amorphous solar cell 8 is designed so that light enters the solar cell through the transparent insulating substrate 1 and is absorbed mainly by the i-type amorphous silicon layer 4. An electromotive force is generated between the two electrodes, the transparent electrically conductive layer 2 and the aluminum electrode 7, and electricity is led out of the solar cell by a conductor 10.
For such an amorphous silicon solar cell, it is most important to improve the photoelectric conversion efficiency. As a method of achieving this, it is known to roughen the surface of the transparent electrically conductive layer. By roughening the surface, incident light is scattered at the interface between the transparent electrically conductive layer and the amorphous silicon semiconductor layer. The effect of this optical scattering is to reduce the surface reflection loss of the incident light and to increase the absorbance in the i-type amorphous silicon layer. As a result of multiple reflection and refraction in the amorphous silicon semiconductor layer, the length of the optical path increases and the light-collecting efficiency of the amorphous silicon solar cell for long wavelength lights will be improved by the light-trapping effect in the i-type amorphous silicon layer. The short-circuit current density will also be increased, thereby improving the power generation efficiency and the photoelectric conversion efficiency.
As specific method for such surface roughening, Japanese unexamined patent publication No. 57756/1983 discloses an average particle size of the surface of the transparent electrically conductive layer from 0.1 to 22.5 .mu.m; Japanese unexamined patent publication No. 201470/1984 discloses the preparation of a transparent electrically conductive layer composed of crystal grains having an average grain size of from 0.1 to 0.9 .mu.m; Japanese unexamined patent publication No. 103384/1984 discloses an average grain size of fine crystals constituting a transparent electrically conductive layer to be at least 300 .ANG.; and Japanese unexamined patent publication No. 175465/1985 discloses forming a silicon oxide coating layer having a haze of at least 1% and having a number of projections having a diameter of from 300 to 500 .ANG. and a height of from 200 to 3,000 .ANG., to obtain a solar cell substrate having a transparent electrically conductive layer.
With solar cell substrates having the above-mentioned structures, it may be possible to increase the photoelectric conversion efficiency to some extent, but they are inadequate for the purpose of greatly improving the efficiency.